Spray-weld alloys



United States Patent SPRAY-WELD ALLOYS Arthur P. Shepard, Flushing, N.Y., assignor to Metallizin Engineering Co. Inc., a corporation of New Jersey No Drawing. Application November 25, 1957 Serial No. 698,378

16 Claims. (Cl. 75-.5)

This invention relates to new and useful improvements in spray-weld alloys and in particular in nickel-base and cobalt-base alloys used in the spray-weld process. Such alloys are known in the art, and they contain boron or boron plus silicon to provide fluxing properties. For this reason these alloys are known as self-fluxing alloys and will be hereinafter referred to as such.

Such alloys are used for Welding and brazing and particularly for coating materials applied as a fused or welded over-lay on base materials, such as steel or steel alloys.

The elements boron and silicon, when added to nickel or nickel base alloys, and cobalt or cobalt base alloys, act as fluxer of the alloy and of the surface to be alloyed during the fusing of the alloy when performing the brazing, welding or coating operation. Boron alone may be used in some cases, but superior fluxing action is usually obtained when both boron and silicon are used.

One process frequently used for applying fused coatings of self-fluxing alloys is known as spray-welding. Spray-Welding comprises the steps of first metal spraying the alloy onto the surface to be coated, and second, fusing the coating in place. The metal spraying operation can be carried out by any of the known metal spraying techniques, in which the material to be sprayed is fed into a heating zone where it is melted or heat-softened and from which it is, in finely divided form, propelled in molten or heat-plastic condition onto the surface to be coated. The material being fed to the heating zone may be in the form of a rod or in the form of a powder, or in some cases, in the form of a powder bonded together by a plastic material to form a wire, said plastic material being of a nature such that it disintegrates in the heat of the flame, releasing the metal particles. In metal spraying methods where the material is fed in the form of a rod or wire, the tip of the Wire is melted in the heating zone and sufficient energy is applied to the tip of the molten wire by a blast of air or other gas, to cause the molten metal at the tip to subdivide into a fine spray.

After coatings have been applied by the metal spraying process, they are thereafter fused in the carrying out of the spray-welding process. Such fusing may be done in a furnace or, alternatively, by means of heating torches applied directly to the coated surface, or by other means such as induction heating.

The self-fluxing alloys heretofore most Widely used in the spray-weld process comprise nickel or nickel-chromium alloys containing boron and silicon.

The extent to which the spray-welding properties of the boron, nickel-base alloy can remain essentially unaffected by the addition of certain alloy components is exemplified by the fact that they may contain from 0% up to 20% Cr by weight of total alloy. This component imparts increasing corrosion and oxidation-resistance properties without interfering with or displacing the essential properties of the alloy.

Elements such as carbon may be present in either nickel base or cobalt base alloys as impurities or as desirable components to increase, for instance, the hardness of the spray-welding alloy. The upper limit of carbon content, however, is dictated by the fact that excessive amounts will impart too high a degree of brittleness to 5 the alloy, thereby interfering with the property of ductility. Another frequently occurring component of these spray-welding boron, nickel-base or cobalt base alloys is iron, which should not be normally present in amounts exceeding and preferably not in amounts exceed- 10 .ing 5% by weight of the total alloy.

-A typical spray-weld alloy of the boron, nickel type,

as an example, consists of 0.7-l% carbon, 35-45% silicon, 2.75-3.75 boron, 3-5% iron, and optionally an additional 16-18% chromium, with nickel making upthe balance.

Some other spray-weld alloys of the boron, nickel type, which have been found suitable for the spray-weld process, are listed in the following table, the amounts indicating percent by weight:

Cobalt base alloys can also be used as self-fluxing alloys for the spray-weld process in place of nickel base alloys. Some typical spray-weld alloys of the boron, cobalt type, or of the boron-cobalt-nickel type, which have been found suitable for the spray-weld process, are listed in the following table:

TABLE Nominal Composition by weight) Such heretofore known alloys have been subject to one serious defect, to more or less degree. This defect is that after fusing, small isolated pores appear occasionally in the coatings and are frequently uncovered by a finishing or grinding operation. Under certain circumstances these pores may have a random distribution and may appear fairly infrequently throughout the coating. Nevertheless, the appearance of even one pore uncovered by the grinding or finishing operation may be a very serious matter, and for many parts for which such coatings are used, such as pump plungers, may render the part totally defective and unusable. It is obvious therefore that even randomly distributed small pores can cause expensive loss of parts, particularly where large areas or a large number of parts are being spray-welded.

Under certain conditons pores in the finished coating may be distributed in systematic arrangements, as the result of the contour of the part being coated and the spraying technique used. In such cases clusters of pores appear at such locations as shaft shoulders or in lines over the grooves of V threads, where threading has been used as a means of undercutting and preparation of the 2,936,229,. Patented May 10, 1 960 base for the application of the coating. In'all such cases Where clusters of pores appear near the surface,

7 they are almost sure to rende'r the finished part defective.

While it has been determined that spraying techniques;

and base preparation techniques, can have an effect upon the number and location of pores produced, no combination of techniques has been discovered which will eliminate pores altogether.

One object of this invention is to provide a spraywelding powder of the self-fluxing' type, which produces pore-free coatings whenused in' the normal operation of:

spray-welding. V 7

It is afurther object of the invention to provide such aspray-welding powder which will produce pore free spray-welded" coatings, even though the coatings are. sprayed under adverse conditions and without strict ad.-

herenceto normal techniques, thereby providing a more trouble-free spray-welding process.

I in powder formv to. produce a powder mixture in which one or more of the constitutents contain sufficientboron or boron and silicon to perform the self-fluxing function for the entire mixture when the mixture is spray-welded. In such cases it is preferred to add the aluminumto one or more of the alloy constituents, such that the percentage of aluminum in the total-mixture of powder is between 0.2 and 2%'.- Alternatively, the aluminum may be added to: such a mixture in theform of a powder or alloyed in another alloy with element or elements which are compatible with such mixture. 7

It has been foundv that at least substantially 0.2% of aluminum is required as an addition by weight of the It is' a further object of the invention to provide such V a' spray wel'ding powder for producing spray-welded coatings; which is not affected by a wide variety ofrelatively adverse base preparationtechniquesand still provide a pore-free alloy coating, thereby providing a more trouble-free spray-welding process.

- It is a still further object of the invention to provide such a. spray-welding powder suitable for producing porefree spray-weldedcoatings and still retain all of the properties normally required of such alloys such as the following properties:

(l) The property of a melting point appreciably below the melting point of the baseto which theyare applied, which is usually steel;

(2.) The property of wetting the surface to which they are applied, which is usually steel; (3) The property of having a relatively wide viscous fluid range with respect to temperature variation so that the coatings will not run. or' drip during the fusing op-- eration;

(4) The property of having a relatively low surface tension to avoid retraction from edges during the fusing operation;

( 5) The property of having sufiicient plasticity at total self-fluxing alloy powder, in accordance with this merely serve the function of eliminating the pores without affecting the powder in any other manner. Amounts of aluminum in excess of about 5% by weight of the powder generally adversely affect the fusing characteristics of the powder. When amounts of aluminum of more than about 2% by weight of the. total powder are used,

the same affects the appearance of the fused coating ulti= matel-y formed, giving the same a dull and tarnished looking surface. Therefore, for many applications it is desirable to use less than 2% "by weight of the aluminum. The preferable range of amount of aluminumis between 0.2-0.4% by weight, since whenused in this amount the temperatures belowbut near the melting point, to avoid undue cracking due toshrinkage during freezing;

(6) The property of having sufficient ductility or. toughness to avoid cracking due to temperature variations. H during cooling; 7

(7- The property of forming anjoxide-dissolving slag separable from the molten metal tol'remove the oxides therefrom, since such oxides formed during spraying or fusing interfere seriously with the coalescence duringfusing and adverselyaffect. the physical properties of the fused coatings;

('8) The property of resistingcorrosive attack of various environments.

' These and still further objects will' become apparent from the following description.

. the spraying and the particular fuelgas.

, Spray-welding powder for use in the spray-welding 7 process in accordance with this invention comprises any conventional spray-welding powder of the self-fluxing type additionally containing a minor quantity of at least 0.2% aluminum. Such aluminum may be either an alloy constituent of the self-fluxing type alloy or added aluminum effectively eliminates the pores without affect- 7 mg the properties of the powder in any other manner.

f In general, however, larger amounts of aluminum may be added without afiecting the other characteristics of the powder when the aluminum is added as an alloying.

element to the-self-fluxing type alloy than when the aluminum is added as aluminum powder in admixture with the remainder of the spray-weld powder.

In cases where the aluminum is alloyed it is often possible to safely use amounts of 0.2-1% without any danger of affecting the normal properties of the powder and without the danger of causing a dulling of the fin-- is hed surface from the spraying and fusing of the coatmg. a

Thespray-weldpowder should in general have a mesh size below U.S.. standard. The exact mesh sizegenerally depends on the particular equipment used for Thus, for example, when using acetylene as the fuel gas, the particles should allbe belowabout' U.S. standard mesh and not more than 15% of the particles should. be below 325 mesh. In contrast to this, when using hydrogen as a fuel 'gas, there is no lower limit as to the mesh size and all the particles may be below 325 mesh, i.e. may be as small as it is physically possible to obtain.

The use of aluminum as a de-oxidant, as an alternative to other well known de-oxidizing materials, by adding it to the melt in the manufactureof alloys of the to the powder in other form, such as in the form of alu minum powder. Alternatively, the aluminum may be added in the form of an alloy or combination with another element or elements, such as, for instance, ferro aluminum; provided that such other element or elements do not adversely affect the performance of the powder mixture in the spray-welding process. It is preferred to add'the aluminumto a 'boron, nickel- 7 base, cobalt-base, ornickel/cobalt-base alloy in the form of an alloying element with a percentage of from 0.2 to 0.4% by weight.

It is sometimes preferred to boron, nickel-base or cobalt-base types has been well known in the .art.. As the result of this practice, small ,traces of aluminum have sometimes appeared in sprayweld alloys of the type used for spray-welding, and in some cases residual. amounts of aluminum resulting from this manufacturing practice have been found in.

percentages up. to substantially 0.1%. In no cases, however, have the residual traces of aluminum, even including those'cases where the residual aluminum has been found in an amount of substantially 0.1%,formed a mixture or alloy which produced pore free spraywelded. coatings.

mix two or more alloys 15 The following are some examples of alloy powders Example 2 Another example of a spray-weld alloy powder in accordance with this invention is a powder substantially all minus 120 mesh U.S. standard screen size and containing not more than 20% minus 325 U.S. standard screen size, the particles of 'the powder being of a boroncobalt type alloy consisting of 0.5-1.5% carbon, 1.5- 25% boron, 4-5% iron, and optionally and additional 26-30% chromium, 0.2-2% aluminum with cobalt making up the balance.

' Example 3 Still another example of a spray-weld alloy powder in accordance with this invention is a powder substantially all minus 120 U.S. standard screen size and containing not more than 20% minus 325 U.S. standard screen size, the powder consisting of a 50%50% mechanical mixture of metal particles of a first and second alloy, the first alloy consisting of 0.71% carbon, 3.5-4.5% silicon, 2.75-3.75% boron, 35% iron, and optionally an additional 16-18% chromium with nickel making up the balance; the second such alloy consisting of l6% silicon, 1-6% boron, 3-8% copper, 310% molybdenum, 0.44% aluminum and optionally an additional 16- 20% chromium, -l% carbon, 0-5% iron with nickel making up the balance. It should be noted that in this particular mixture of powder alloys, the percentage of the aluminum appearing in the m xture in accordance with the invention is 0.2-2%, due to the fact that it occurs in one 50% constituent in the range 0.44%.

Example 4 Still another example of a spray-weld alloy powder in accordance with this invention is a powder substantially all minus 120 mesh U.S. standard screen size and containing not more than 20% minus 325 U.S. standard screen size, the particles of the powder being a mixture of powder particles of a boron, nickel type alloy, consisting of 4-5 silicon, 3.54.5% boron, 5-6% copper, 4.55.5% molybdenum, 8l2% chromium, 0-0.2% carbon, 05% iron with nickel making up the balance; and a pure powder aluminum in sufficient quantity to provide 0.2-2% by weight of the entire mixture.

The following example illustrates the use of a sprayweld powder in accordance with this invention:

Example 5 One alloy in accordance with this invention has the following analysis:

In one method of applying the alloy exemplified by the above specified analysis, it is subdivided so that it with this in-- 6 will all pass through a 120 mesh standard screen and applied by means of conventional-powder-metal spray gun. As a specific example of this application, a steel shaft having a 2" diameter section 4" long, and with a key-way ,4 x ,4,," x 1" long at one end of the section to be sprayed, is prepared for the spray-welding operation by first machining the surface to be coated with a V-thread approximately 30 threads to the inch and with a depth of approximately 75% of full U.S. .standard depth and thereafter grit-blasting with a conventional blast machine, in which the grit is blown forcibly against the surface of the shaft by means of compressed air, using S.A.E.G. -16 crushed steel grit and a blast air pressure of 100 p.s.i. for a few minutes, sufliciently to.

roughen and thoroughly clean the surface to be coated. A steel key, A square, is fitted into, the keyway of the shaft before blasting.

A coating of A; thickness of the alloy is metal-sprayed in conventional manner over the entire shaft section to be coated while the shaft is rotated in a lathe. The key is then removed by grinding away the edges of the sprayed coating adjacent the key and tapping the key out of the keyway. 1

While rotating the shaft in alathe, the shaft is preheated, using a conventional oxy-acetylene heating torch over the entire coated section, to a'temperature of approximately 1000 F. The torch is then concentrated at one end of the coated section while the shaft is still rotating, so as to raise the temperature of a small band of the coating. As the coating fuses, the torch is gradually moved along the coated section of the shaft so as to successively fuse each small band of the coating until the entire coating has been fused. The heating is then stopped and the shaft allowed to cool in air and without any attempt at controlled cooling or heat-insulation.

The coated end of the shaft is then ground to a diameter of approximately 2 The coating will shrink about 20% during fusing from the original sprayed thickness of 4;". This will still leave sufiicient finish allowance for grinding the coating to a finished thickness of approximately on a side of the shaft.

The coating thus applied was found to be completely finish-ground on the diameter, have a relatively small radius on the corner at the edge of the keyway, be firmly adherent at the edges of the keyway, as well as elsewhere, and be free from pores in its entire surface.

The spray-weld powder in accordance with this invention is for use in a metal spray gun and may ordinarily be used in a powder type metal spray gun directly without further treatment. However, if it is desired to use the powder in accordance with the invention in a wire type metal spray gun, this may be done, in accordance with known practice as previously described, by binding the particles of powder together with a suitable plastic binder in the form of a rod or Wire. The term powder" is used in the claims to generally designate the powder both in loose form and in bound form as for example in the form of a rod or wire.

Example 6 Example 5 was repeated except prior to use, the powder was intimately mixed and dispersed in a melt of high intention that the invention be limited only by the, appended claims or their equivalents wherein I have endeavored to claim broadly all inherent novelty.

- mem f claim.

- 1 In a sprawweldable, self fluxing' metal powder essenmay consisting of a base metal selected from the group consistingof nickel, cobalt and combinations thereof, and p 1 containing boron as the sel'f-fluxin'g element, the im-- provement which comprises the powder additionally containing about 0.2 by weight of aluminum;

2. Improvement according to claim 1 in which: said 7 aluminum i's'alloyed with atleast one other constituent of saidpowd'eri 3'; Improvement according to claim 1 in which said aluminum is present in unall'oyed divided form.

4. Improvement according toclaim 1 in which' the metal powder has a particle size below about d mesh.

' '5. Ina spray-weldable, self-fluxing nickel base alloy.

metal powder containing boron as ,the-self-fluxing element, the improvement which comprises the alloyed'm-etal powder additionally" containing about 0.2 5%: by weight of aluminum, 7 2

6; Improvement according toclaim. 5 in which said aluminum is present in amount ofabout 0.2-2% by Weight.

1 7. Improvement according to claim 5 in whichsaid aluminum i's 'alloyed with at least one. of the other consti tuents of said powder. a

Improvement according to claim 5 in which said aluminum ispresent in an: unalloyed, divided form.

9 Improvement according to claim 5 in which said powder has a particle size: below about 100 mesh.

10. In a spray-weldable, self-fluxing nickel-cobalt base alloy" metal powder containing.- boron as'the self-fluxing. element-, the improvement which comprises the alloy metal powder additionally containing about 012-5 by weight of aluminum.

11*; In asp'rayaweldable, self-fluxing cobalt base alloy metal powder containing: boron asv the. self-fluxing element, the improvement which: comprises the alloy metal powder additionally containing about' 0.'2:- 5% by weight:

of aluminum.

12. Improvement accordingsto claim 11 in which said aluminum-is present in. amount. of about=0.2,-2.%, by weight... A

13. Improvement. according to claim 11 iii which.

aluminum is. present. inv unalloyed, divided-form.

114'. Improvement according. toclaim 11 in which said powder has a particle .size below about mesh.

15. A spray-weldabl'e alloy p'owder'of the nickel. base type comprising 0.7 1% carbon, 315-415 silicon, 2.7 5- 3.75%' boron, 3'5% iron, up to [8 chromium, -0.Z-2% aluminum and nickel making up'the balance;

16. A spray-weldable alloy powder of the cobalt base type comprisingO.5-1.5% carbon, 1.5-2.5 boron,.4-5-% iron, up to. 30 chromium, 0';22% aluminum and co balt making up the balance. i i

References Cited in the file of this patent" UNITED STATES; PATENTS OTHER. REFERENCES I Holgatei Electroplating and Metal Spraying, VOL 7', No;

6, June 1954, pages" 239-242 and 245. Published by Robert Draper,'Ltd., Teddington, Mid'dx., England. 

1. IN A SPRAY-WELDABLE, SELF-FLUXING METAL POWDER ESSENTIALLY CONSISTING OF A BASE METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL, COBALT AND COMBINATION THEREOF, AND CONTAINING BORON AS THE SELF-FLUXING ELEMENT, THE IMPROVEMENT WHICH COMPRISES THE POWER ADDITIONALLY CONTAINING ABOUT 0.2-5% WEIGHT OF ALUMINUM. 